The ultimate objective of this work is to understand how cell growth is regulated using the model unicell Chlamydomonas. Defects in cell growth regulation in humans have been linked to Peutz-Jeghers syndrome, Cowdens's disease and other cancers marked by unorganized cell growth. Genomic information indicates that the mechanisms for cell growth regulation are common to all eukaryotes; thus insights into cell growth regulation from one model organism can impact the paradigms controlling approaches to human health. During the period of this fellowship, biochemical approaches will be used to characterize the activity and identify novel binding partners of the major cell growth regulator TOR. Using targeted protein labeling the role of TOR in coordinating cytoplasmic and chloroplast growth will be investigated, and using the growth inhibitor rapamycin, genetic approaches will be used to identify components of the growth signaling pathway. By examining the cell growth machinery in a single-celled photosynthetic organism, this work will address questions of the coordination of cytoplasmic and chloroplast growth; simultaneously, it will yield insights into how cell growth is regulated in all eukaryotes. [unreadable] [unreadable] [unreadable]